Qirong Liu

In situ electrochromic efficiency of a nickel oxide thin film: origin of electrochemical process and electrochromic degradation

Electrochromic nickel oxide (NiOx) thin films are one of the most promising anodic colored materials. However, there is lack of accurate description of their electrochemical process and degradation mechanism. In this study, a novel approach involving in situ electrochromic efficiency is proposed to reveal the electrochemical origin of an electrochromic NiOx thin film cycled in a Li+-ion electrolyte. The results indicate that the coloring process of the NiOx thin film refers to the oxidation reactions of Ni2+ to Ni3+ and Ni2+ to Ni4+ (in two forms of Ni3O4 and Ni2O3), and the bleaching process is associated with the reduction reactions of Ni4+ to Ni2+, Ni4+ to Ni3+, and Ni3+ to Ni2+. The irreversible reduction of Ni4+ to Ni3+ plays a dominant role in the activation procedure of NiOx. It is deduced that the Li+-ion trapping in the bleaching process along with the reduction reactions of Ni4+ to Ni3+ and Ni3+ to Ni2+ causes the degradation of the electrochromic properties. This study provides a further insight into the electrochromic mechanism and is conducive to the improvement of the long-term cyclic durability for Li+-based electrochromic NiOx. Moreover, the study significantly establishes a direct connection between an electrochemical process and a variation in the optical absorbance of materials.

Optical, electrical, and electrochemical properties of indium tin oxide thin films studied in different layer-structures and their corresponding inorganic all-thin-film solid-state electrochromic devices

In this investigation, the indium tin oxide (ITO) film layers were prepared by reactive direct current magnetron sputtering at room temperature with different deposition parameters on six different substrates: glass, polyethylene terephthalate (PET), NiOx/ITO/glass, NiOx/ITO/PET, WO3/ITO/glass, and WO3/ITO/PET. The ITO deposited on WO3/ITO/glass showed great advantage than others having a resistance as low as 9.2 Ω/◻ and a high average optical transmittance of 77.1% and reaching the balance between the optical and electrical properties of ITO thin films. Meanwhile, the WO3 film as electrochromism layer on ITO (under different deposited parameters)/glass shows nearly perfect reversibility, charge density of 20 mC/cm2, and fast response time of about 2–6 s. With the outer ITO thin film layer optimized, the electrochromic devices (ECDs) with typical five-layer structure were deposited. ECDs show the reversible dark-blue-coloration and bleaching cycles, large optical contrast, fast response time, and good sta...

Electro-optical performance of inorganic monolithic electrochromic device with a pulsed DC sputtered Li x Mg y N ion conductor

Lithium magnesium nitride (LixMgyN) thin films were deposited by pulsed DC reactive magnetron sputtering from a LiMg alloy target in the mixture gas of Ar and N2. The as-prepared LixMgyN films were amorphous. A monolithic inorganic electrochromic device (ECD) based on WO3/NiO complementary structure was fabricated using the LixMgyN as the ion conductor layer. The addition of a 150-nm thick Si3N4 buffer layer between LixMgyN and NiO made coloration and bleaching reversible and stable. Electrochemical and optical characterizations were conducted to evaluate the performance of the ECD. Electro-optical data were recorded for both 1000 chronoamperometric cycles and 1000 voltammetric cycles. Activation and degradation of the electro-optical properties of the ECD were observed.

Robust Sandwich-Structured Nanofluidic Diodes Modulating Ionic Transport for an Enhanced Electrochromic Performance

Abstract Biomimetic solid‐state nanofluidic diodes have attracted extensive research interest due to the possible applications in various fields, such as biosensing, energy conversion, and nanofluidic circuits. However, contributions of exterior surface to the transmembrane ionic transport are often ignored, which can be a crucial factor for ion rectification behavior. Herein, a rational design of robust sandwich‐structured nanofluidic diode is shown by creating opposite charges on the exterior surfaces of a nanoporous membrane using inorganic oxides with distinct isoelectric points. Potential‐induced changes in ion concentration within the nanopores lead to a current rectification; the results are subsequently supported by a theoretical simulation. Except for providing surface charges, functional inorganic oxides used in this work are complementary electrochromic materials. Hence, the sandwich‐structured nanofluidic diode is further developed into an electrochromic membrane exhibiting a visual color change in response to redox potentials. The results show that the surface‐charge‐governed ionic transport and the nanoporous structure facilitate the migration of Li+ ions, which in turn enhance the electrochromic performance. It is envisioned that this work will create new avenues to design and optimize nanofluidic diodes and electrochromic devices.